With long migrations, many birds fly for days without landing for a rest and it has been often speculated that some species of birds have the ability to sleep whilst in flight.

A team of researchers from the Max Planck Institute for Ornithology in Germany decided to fit brain activity monitors to 15 frigatebirds over the course of 10 days and 3000 miles of flight time in the attempt to finally find out the real sleep patterns of our feathery friends.

The study found birds are able to sleep during flight to varying degrees by using different parts of their brain. By shutting down or resting one part of their brain, they are able to maintain alertness in another area. This was found mainly in the eye-facing area of the brain which stayed alert.

Interestingly, the team also found that for very short periods whilst flying, birds are able to enter a deep sleep or REM without any affect on their flying duration. Lead author, Niels Rattenborg in correspondence with Christian Science Monitor, says the finding was unexpected.

“Most people assumed that birds sleep unihemispherically in flight. However, the frigatebirds also sometimes slept with both halves of the brain at the same time.”

What is now being questioned is the amount of sleep these birds need. They are seemingly able to survive with very little rest time which, in humans, would lead to cognitive deterioration. Despite long journeys, some migrating birds still don’t take a lot of time to nap while in flight.

“Previous laboratory studies have shown that pigeons can stay awake for weeks without visible health problems, contrary to rats which will die under identical conditions,” states co-author Dr. Vyssotski. “A surprising conclusion has been derived, that birds are lacking so-called ‘sleep-deprivation syndrome.”

More research will go into finding out why some species need more sleep than others and the consequences of lack of sleep and functioning abilities.

The details of the study were published in the journal Nature Communications.